Fuzzy ideals of K-algebras

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1 Annals of University of Craiova, Math. Comp. Sci. Ser. Volume 34, 2007, Pages ISSN: Fuzzy ideals of K-algebras Muhammad Akram and Karamat H. Dar Abstract. The fuzzy setting of an ideal in a K-algebra is presented and some properties are investigated. Properties of homomorphic image and inverse image of fuzzy ideals of K-algebras are discussed. A characterization theorem of fuzzy fully invariant is given. Fuzzy relations on K-algebras are discussed. A characterization theorem of fuzzy ideals in terms of the strongest fuzzy relations on K-algebras is also studied Mathematics Subject Classification. 06F35, 03G25, 03B52. Key words and phrases. K-algebras; Ideals; Fully invariant; Fuzzy relations; Strongest fuzzy relations. 1. Introduction A K-algebra (G,,, e), introduced by Dar and Akram [4], is an algebra built on a group (G,, e) with identity e and adjoined with an induced binary operation on G. It is non-commutative and non-associative with a right identity e. It is proved in [2, 4] that a K-algebra on an abelian group is equivalent to a p-semisimple BCI-algebra. For the convenience of study, authors renamed a K-algebra built on a group G as a K(G)-algebra [5]. The K(G)-algebra has been characterized by using its left and right mappings in [5]. Recently, Dar and Akram [7] have further proved that the class of K(G)-algebras is a generalized class of B-algebras [12] when (G,, e) is a non-abelian group, and they also proved that the K(G)-algebra is a generalized class of the class of BCH/BCI/BCK-algebras [8, 9, 10] when (G,, e) is an abelian group. After the introduction of fuzzy sets by Zadeh [14], the fuzzy set theory developed by Zadeh himself and others in many directions and found applications in various areas of sciences. The study of fuzzy algebraic structures started with introduction of the concept of the fuzzy subgroup of a group in the pioneering paper of Rosenfeld [13]. Since then many researchers have been engaged in extending the concepts and results of abstract algebra to broader framework of the fuzzy setting. Akram et al. introduced the notions of subalgebras and fuzzy (maximal) ideals of K-algebras in [1] and further studied by Jun et al. in [11]. As a continuation of [1, 11], further some properties of the fuzzy ideals in a K-algebra are investigated. Properties of homomorphic image and inverse image of fuzzy ideals of K-algebras are discussed. A characterization theorem of fuzzy fully invariant is given. Fuzzy relations on a K-algebra are also discussed. Received: February 13, This research work of the first author is supported by PUCIT, Pakistan. The second author is supported by HEC-Islamabad, Pakistan. 11

2 12 M. AKRAM AND K.H. DAR 2. Preliminaries In this section we review some elementary aspects that are necessary for this paper: Let (G,, e) be a group with the identity e such that x 2 e for some x( e) G. A K-algebra built on G (briefly, K-algebra) is a structure K = (G,,, e), where is a binary operation on G which is induced from the operation, that satisfies the following: (k1) ( a, x, y G) ((a x) (a y) = (a (y 1 x 1 )) a), (k2) ( a, x G) (a (a x) = (a x 1 ) a), (k3) ( a G) (a a = e), (k4) ( a G) (a e = a), (k5) ( a G) (e a = a 1 ). If G is abelian, then conditions (k1) and (k2) are replaced by: (k1 ) ( a, x, y G) ((a x) (a y) = y x), (k2 ) ( a, x G) (a (a x) = x), respectively. A nonempty subset H of a K-algebra K is called a subalgebra of K if it satisfies: ( a, b H) (a b H). Note that every subalgebra of a K-algebra K contains the identity e of the group (G, ). A mapping f : K 1 K 2 of K-algebras is called a homomorphism if f(x y) = f(x) f(y) for all x, y K 1. Note that if f is a homomorphism, then f(e) = e. A nonempty subset I of a K-algebra K is called an ideal of K if it satisfies: (i) e I, (ii) ( x, y G) (x y I, y (y x) I x I). Let µ be a fuzzy set on G, i.e., a map µ : G [0, 1]. A fuzzy set µ in a K-algebra K is called a fuzzy subalgebra of K if it satisfies: ( x, y G) (µ(x y) min{µ(x), µ(y)}). Note that every fuzzy subalgebra µ of a K-algebra K satisfies the following inequality: ( x G) (µ(e) µ(x)). 3. Fuzzy ideals of K-algebra Definition 3.1. A fuzzy set µ in a K-algebra K is called a fuzzy ideal of K if it satisfies: (i) ( x G) (µ(e) µ(x)), (ii) ( x, y G) (µ(x) min{µ(x y), µ(y (y x))}). Example 3.1. Consider the K-algebra K = (G,,, e) on the cyclic group G = {0, a, b, c, d, f}, where 0 = e, a = a, b = a 2, c = a 3, d = a 4, f = a 5 and is given by the following Cayley s table: 0 a b c d f 0 0 f d c b a a a 0 f d c b b b a 0 f d c c c b a 0 f d d d c b a 0 f f f d c b a 0

3 FUZZY IDEALS OF K-ALGEBRAS 13 Let µ be a fuzzy set in G defined by µ(e) = t 1 and µ(x) = t 2 for all x 0 in G, where t 1 > t 2 in [0, 1]. Then, by routine verification, it is easy to see that µ is a fuzzy ideal of K. The following propositions are obvious. Proposition 3.1. [1] Let µ be a fuzzy set in a K-algebra K. Then µ is a fuzzy ideal of K if and only if the set U(µ; t) := {x G µ(x) t}, t [0, 1], is an ideal of K when it is nonempty. Proposition 3.2. Let µ be a fuzzy ideal of a K-algebra K and let x K. µ(x) = t if and only if x U(µ; t) and x / U(µ; s) for all s > t. Then Proposition 3.3. If µ and λ are fuzzy ideals of K. Then µ λ is also a fuzzy ideals of K. Definition 3.2. For a family of fuzzy sets {µ i i I} in a K-algebra K, define the join i I µ i and meet i I µ i of {µ i i I} as follows: ( i I µ i )(x) = sup{µ i (x) i I}, for each x G. ( i I µ i )(x) = inf{µ i (x) i I} Theorem 3.1. The family of fuzzy ideals of K is a completely distributive lattice with respect to the meet and the join. Proof. Let {µ i i I} be a family of fuzzy ideals of K. Since [0, 1] is a completely distributive lattice with respect to the usual ordering in [0, 1], it is sufficient to show that i I µ i and i I µ i are fuzzy ideals of K. For any x K, and Let x, y K. Then ( i I µ i )(e) = sup i I µ i (e) sup µ i (x) = ( µ i )(x), i I i I ( µ i )(e) = inf µ i(e) inf µ i(x) = ( µ i )(x). i I i I i I i I ( µ i )(x) = sup{µ i (x) i I} sup{max(µ i (x y), µ i (y (y x))) i I} = max(sup{µ i (x y) i I}, sup{µ i (y (y x)) i I}) = max(( µ i )(x y), ( µ i )(y (y x))), ( µ i )(x) = inf{µ i (x) i I} inf{min(µ i (x y), µ i (y (y x))) i I} = min(inf{µ i (x y) i I}, inf{µ i (y (y x)) i I}) = min(( µ i )(x y), ( µ i )(y (y x))). Hence I µ i and i I µ i are fuzzy ideals of K. Theorem 3.2. If µ is a fuzzy ideal of a K-algebra K, then for all x G µ(x) = sup{t [0, 1] x U(µ; t)}.

4 14 M. AKRAM AND K.H. DAR Proof. Let s := sup{t [0, 1] x U(µ; t)}, and let ɛ > 0. Then s ɛ < t for some t [0, 1] such that x U(µ; t), and so s ɛ < µ(x). Since ɛ is an arbitrary, it follows that s µ(x). Now let µ(x) = v, then x U(µ; v) and so v {t [0, 1] x U(µ; t)}. Thus µ(x) = v sup{t [0, 1] x U(µ; t)} = s. Hence µ(x) = s. This completes the proof. We now consider the converse of Theorem 3.2. Theorem 3.3. Let Ω be a nonempty finite subset of [0, 1]. Let {G w w Ω} be a collection of ideals of a K-algebra K such that (i) G = w Ω G w, (ii) α > β if and only if G α G β for all α, β Ω. Then a fuzzy set µ in G defined by is a fuzzy ideal of K. µ(x) = sup{w Ω x G w } Proof. In view of Proposition 3.1, it is sufficient to show that every nonempty level set U(µ; α) is an ideal of K. Assume U(µ; α) α for some α [0; 1]. Then the following cases arise: 1. α = sup{β Ω β < α} = sup{β Ω G α G β }, 2. α sup{β Ω β < α} = sup{β Ω G α G β }. Case(1) implies that x U(µ; α) x G w w < α x G w. Hence U(µ; α) = w<α G w, which is an ideal of K. For case (2), there exists ɛ > 0 such that (α ɛ, α) Ω =. We claim that in this case U(µ; α) = β α G β. Indeed, if x β α G β, then x G β for some β α, which gives µ(x) β α. Thus x U(µ; α), i.e., β α G β U(µ; α). On the other hand, if x / β α G β, then x / G β for all β α, which implies that x / G β for all β > α ɛ, i.e., if x G β then β α ɛ. Thus µ(x) α ɛ. So x / U(µ; α). Thus U(µ; α) β α G β. Hence U(µ; α) = β α G β, which is an ideal of K. This completes the proof. Theorem 3.4. Let f : K 1 K 2 be an epimorphism of K-algebras. If ν is a fuzzy ideal of K 2 and µ is the pre-image of ν under f. Then µ is a fuzzy ideal of K 1. w<α Proof. It is easy to see that µ(e) µ(x) for all x K 1. For any x, y K 1, µ(x) = ν(f(x)) min(ν(f(x y)), ν(f(y (y x)))) Hence µ is a fuzzy ideal of K 1. = min(µ(x y), µ(y (y x))). Definition 3.3. Let K 1 and K 2 be two K-algebras and let f be a function from K 1 into K 2. If ν is a fuzzy set in K 2, then the preimage of ν under f is the fuzzy set in K 1 defined by f 1 (ν)(x) = ν(f(x)) x G. Theorem 3.5. Let f : K 1 K 2 be an epimorphism of K-algebras. If ν is a fuzzy ideal in K 2, then f 1 (ν) is a fuzzy ideal in K 1.

5 FUZZY IDEALS OF K-ALGEBRAS 15 Proof. It is easy to see that f 1 (ν)(e) f 1 (ν)(x) for all x K. Let x, y K, then f 1 (ν)(x) = ν(f(x)) min(ν(f(x y), f(y (y x))) = min(ν(f(x y)), ν(f(y (y x)))) = min(f 1 (ν)(x y), f 1 (ν)(y (y x))). Hence f 1 (ν) is a fuzzy ideal in K 1. Definition 3.4. Let a mapping f : K 1 K 2 from K 1 into K 2 of K-algebras and let µ be a fuzzy set of K 2. The map µ f is called the pre-image of µ under f, if µ f (x) = µ(f(x)), for all x G. Theorem 3.6. Let f : K 1 K 2 be an epimorphism of K-algebras. If µ is a fuzzy ideal of K 2, then µ f is a fuzzy ideal of K 1. Proof. For any x K, we have µ f (e 1 ) = µ(f(e 1 )) = µ(e 2 ) µ(f(x)) = µ f (x). For any x, y K, since µ is a fuzzy ideal of K 1, µ f (x) = µ(f(x)) min{µ(f(x y)), µ(f(y) f(y x))} = min{µ(f((x y)), µ(f(y (y x)))} = min{µ f ((x y)), µ f (y (y x))} proving that µ f is a fuzzy ideal of K 1. Theorem 3.7. Let f : K 1 K 2 be an epimorphism of K-algebras. If µ f is a fuzzy ideal of K 2, then µ is a fuzzy ideal of K 1. Proof. Since there exists x K 1 such that y = f(x) for any y K 2, µ(y) = µ(f(x)) = µ f (x) µ f (e 1 ) = µ(f(e 1 )) = µ(e 2 ). For any x, y K 2, there exist a, b, c K 1 such that x = f(a) and y = f(b). It follows that µ(x) = µ(f(a)) = µ f (a) min{µ f ((a b)), µ f (b (b a))} = min{µ(f(a b)), µ(f(b (b a)))} = min{µ((f(a) f(b))), µ(f(b) (f(b) f(a)))} = min{µ((x y)), µ(y (y x))} proving that µ is a fuzzy ideal of K 1. Definition 3.5. An ideal H of K-algebra is said to be fully invariant if f(h) H, for all f End(K), where End(K) is the set of all endomorphisms of a K-algebra K. A fuzzy ideal µ of a K-algebra K is called a fuzzy fully invariant if µ f (x) µ(x) for all x G and f End(K). Theorem 3.8. A fuzzy ideal is fully invariant if and only if each its level set is a fully invariant ideal.

6 16 M. AKRAM AND K.H. DAR Proof. Suppose that µ is fuzzy fully invariant and let t Im(µ), f End(K) and x U(µ, t). Then µ f (x) µ(x) t µ(f(x)) t f(x) U(µ; t). Thus f(u(µ; t)) U(µ; t), i.e., U(µ; t) is fully invariant. Conversely, suppose that each level ideal of µ is fully invariant and let x G, f End(K) and µ(x) = t. Then, by virtue of Proposition 3.2, x U(µ; t) and x / U(µ; s), for all s > t. It follows from the assumption that f(x) f(u(µ; t)) U(µ; t), so that µ f (x) µ(x) t. Let s = µ f (x) and assume that s > t. Then f(x) U(µ; s) = f(u(µ; s)), which implies from the injectivity of f that x U(µ; s), a contradiction. Hence µ f (x) = µ(f(x)) µ(x) = t showing that µ is fuzzy fully invariant. Definition 3.6. Let µ be a fuzzy ideal of K-algebra K and x K. The fuzzy subset µ x of K defined by µ x(a) = µ(a x) a K is termed as the fuzzy coset determined by x and µ. Proposition 3.4. Let µ be a fuzzy ideal of K. Then K/µ, the set of all fuzzy cosets of µ in K, is a K-algebra under the following operation: µ x µ y = µ x y x, y K. Proof. Straightforward. Theorem 3.9. Let f : K 1 K 2 be homomorphism of K-algebras and let µ be fuzzy ideal of K 1 and λ of K 2 such that f(µ) λ, there is a homomorphism of K-algebras f : K 1 /µ K 2 /λ where f (µ x) = λ f(x) such that the following diagram commutes. K 1 f K 2. K 1 µ K 2 f λ Proof. Let µ x = µ y then µ(x y) = µ(e). Thus λ(f(x) f(y)) = λ(f(x y)) = f 1 (λ)(x y) µ(x y) = µ(e). That is λ(f(x)) = λ(f(y)). Hence f is well-defined. Finally, f is homomorphism because f (µ x µ y) = f (µ x y) = λ f(x) f(y) = λ f(x) λ f(y) = f (µ x) f (λ f(y) ). This completes the proof.

7 FUZZY IDEALS OF K-ALGEBRAS Cartesian product of fuzzy ideals Definition 4.1. [3] A fuzzy relation on any set G is a fuzzy set µ : G G [0, 1]. Definition 4.2. [3] If µ is a fuzzy relation on a set G and λ is a fuzzy set in G, then µ is a fuzzy relation on λ if µ(x, y) min{λ(x), λ(y)} x, y G. Definition 4.3. [3] Let µ and λ be the fuzzy sets in a set G. The cartesian product of µ and λ is defined by (µ λ)(x, y) = min{µ(x), λ(x)}, x, y G. Lemma 4.1. [3] Let µ and λ be fuzzy sets in a set G. Then (i) µ λ is a fuzzy relation on G, (ii) U(µ λ; t) = U(µ; t) U(λ; t) for all t [0, 1]. Definition 4.4. [3] Let λ be a fuzzy set in a set G, the strongest fuzzy relation on G that is fuzzy relation on λ is µ λ, given by µ λ (x, y) = min{λ(x), λ(y)} for all x, y G. Lemma 4.2. [3] For a given fuzzy set λ in a set G, let µ λ be the strongest fuzzy relation on G. Then U(µ λ ; t) = U(λ; t) U(λ; t) for t [0, 1]. Proposition 4.1. For a given fuzzy set λ in a set G, let µ λ be the strongest fuzzy relation on G. If µ λ is a fuzzy ideal of K K, then λ(x) λ(e) for all x K. Proof. If µ λ is a fuzzy ideal of K K, then µ λ (x, x) µ λ (e, e) for all x K. This means that min{λ(x), λ(x)} min{λ(e), λ(e)}, which implies that λ(x) λ(e). Proposition 4.2. If µ λ is a fuzzy ideal of a K-algebra K, then the level ideals of µ λ are given by U(µ λ ; t) = U(λ; t) U(λ; t) for all t [0, 1]. Proof. Follows immediately from Lemma 4.2. Theorem 4.1. If µ and λ are fuzzy ideals of a K-algebra K. Then µ λ is a fuzzy ideal of K K. Proof. For any (x, y) K K, we have (µ λ)(e, e) = min{µ(e), λ(e)} min{µ(x), λ(y)} = (µ λ)(x, y). Let x = (x 1, x 2 ) and y = (y 1, y 2 ) K K. Then (µ λ)(x) = (µ λ)((x 1, x 2 )) = min{µ(x 1 ), λ(x 2 )} Hence µ λ is a fuzzy K-ideal of K K. min{min{µ(x 1 y 1 ), µ(y 1 (y 1 x 1 ))}, min{λ(x 2 y 2 ), λ(y 2 (y 2 x 2 ))}} = min{min{µ(x 1 y 1 ), λ(x 2 y 2 )}, min{µ(y 1 (y 1 x 1 )), λ(y 2 (y 2 x 2 ))}} = min{(µ λ)((x 1 y 1, x 2 y 2 )), (µ λ)((y 1 (y 1 x 1 )), y 2 (y 2 x 2 ))} = min{(µ λ)((x 1, x 2 ) (y 1, y 2 )), (µ λ)((y 1, y 2 ) ((y 1, y 2 ) (x 1, x 2 )))} = min{(µ λ)(x y), (µ λ)(y (y x))}.

8 18 M. AKRAM AND K.H. DAR The converse of Theorem 4.1 may not be true as seen in the following example. Example 4.1. Let K be a K-algebra and let s, t [0, 1) such that s t. Define fuzzy sets µ 1 and µ 2 in K by µ 1 (x) = s and { t if x = 0, µ 2 (x) = 1 otherwise, for all x K, respectively. If x 0, then µ 2 (x) = 1, and thus (µ 1 µ 2 )(x, x) = min(µ 1 (x), µ 2 (x)) = min(s, 1) = s. If x = 0, then µ 2 (x) = t < 1, and thus (µ 1 µ 2 )(x, x) = min(µ 1 (x), µ 2 (x)) = min(s, t) = s. That is, µ 1 µ 2 is a constant function and so µ 1 µ 2 is a fuzzy ideal of K K. Now µ 1 is a fuzzy ideal of K, but µ 2 is not a fuzzy ideal of K since for x 0, we have µ 2 (0) = t < 1 = µ 2 (x). Theorem 4.2. Let µ and λ be fuzzy sets in a K-algebra K such that µ λ is a fuzzy ideal of K K, then (i) Either µ(e) µ(x) or λ(e) λ(x), x K. (ii) If µ(e) µ(x), x K, then either λ(e) µ(x) or λ(e) λ(x). (iii) If λ(e) λ(x), x K, then either µ(e) µ(x) or µ(e) λ(x). (iv) If µ(x) µ(e) for all x K and λ(y) > µ(e) for some y K, then µ is a fuzzy ideal ideal of K. (v) If λ(x) µ(e) for any x K, then λ is a fuzzy ideal of K. Proof. (i) We prove it using reductio ad absurdum. Assume µ(x) > µ(e) and λ(y) > λ(e), for some x, y K. Then (µ λ)(x, y) = min{µ(x), λ(y)} > min{µ(e), λ(e)} = (µ λ)(e, e) (µ λ)(x, y) > (µ λ)(e, e), x, y K, which is a contradiction. Hence (i) is proved. (ii) Again, we use reduction to absurdity. Assume λ(e) < µ(x) and λ(e) < λ(y), x, y K. Then, (µ λ)(e, e) = min{µ(e), λ(e)} = λ(e), (µ λ)(x, y) = min{µ(x), λ(y)} > λ(e) = (µ λ)(e, e) (µ λ)(x, y) > (µ λ)(e, e), which is a contradiction. Hence (ii) is proved. (iii) The proof is similar to (ii). (iv) Assume that µ(x) µ(e) for all x K and λ(y) > µ(e) for some y K. Then λ(e) λ(y) > µ(e). Since µ(e) µ(x) for all x K, it follows that λ(e) > µ(x) for all x K. So Thus (µ λ)(x, e) = min{µ(x), λ(x)} = µ(x) x K. µ(x) = (µ λ)(x, e) min{(µ λ)(x y, e), (µ λ)(y (y x), e)} = min{µ(x y), µ(y (y x))}. Hence µ is a fuzzy ideal of K.

9 FUZZY IDEALS OF K-ALGEBRAS 19 (v) If λ(x) µ(x) for any x K, then λ(x) = min{µ(e), λ(x)} = (µ λ)(e, x) min{(µ λ)(e, x y), (µ λ)(e, y (y x))} = min{min{µ(e), λ(x y)}, min{µ(e), λ(y (y x))}} = min{λ(x y), λ(y (y x))}. Hence λ is a fuzzy ideal of K. The counter example 4.1 shows: if µ λ is a fuzzy ideal of K K, then µ and λ may not be both fuzzy ideals of K. Now we give the partial converse of the Theorem 4.1 is the following Theorem. Theorem 4.3. If µ λ is a fuzzy ideal of K K, then either µ or λ is a fuzzy ideal of K. Proof. By Theorem 4.2(i), without loss of generality we assume that λ(e) λ(x), x K. It follows from Theorem 4.2(iii) that either µ(e) µ(x) or µ(e) λ(x). If µ(e) λ(x), x K. Then (µ λ)(e, x) = min{µ(e), λ(x)} = λ(x) (I) Since µ λ is a fuzzy ideal of K K, (µ λ)(x 1, x 2 ) min{(µ λ)((x 1, x 2 ) (y 1, y 2 )), (µ λ)((y 1, y 2 ) ((y 1, y 2 ) (x 1, x 2 )))}. It implies that (µ λ)(x 1, x 2 ) min{(µ λ)((x 1 y 1, x 2 y 2 )), (µ λ)(y 1 (y 1 x 1 ), y 2 (y 2 x 2 ))}. Putting x 1 =y 1 = e gives (µ λ)(e, x 2 ) min{(µ λ)((e, x 2 y 2 )), (µ λ)(e, y 2 (y 2 x 2 ))}. Using equation(i), we have λ(x 2 ) min{λ(x 2 y 2 ), λ(y 2 (y 2 x 2 ))}. This proves that λ is a fuzzy ideal of K. The second part is similar. This completes the proof. Theorem 4.4. Let λ be a fuzzy set in a K-algebra K and µ λ be the strongest fuzzy relation on K. Then λ is a fuzzy ideal of K if and only if µ λ is a fuzzy ideal of K K. Proof. Suppose that λ is a fuzzy ideal of K. Then µ λ (e, e) = min{λ(e), λ(e)} min{λ(x), λ(y)} = µ λ (x, y) (x, y) K K. For any x = (x 1, x 2 ) and y = (y 1, y 2 ) K K, µ λ (x) = µ λ (x 1, x 2 ) = min{λ(x 1 ), λ(x 2 )} min{min{λ(x 1 y 1 ), λ(y 1 (y 1 x 1 ))}, min{λ(x 2 y 2 ), λ(y 2 (y 2 x 2 ))}} = min{min{λ(x 1 y 1 ), λ(x 2 y 2 )}, min{λ(y 1 (y 1 x 1 )), λ(y 2 (y 2 x 2 ))}} = min{µ λ (x 1 y 1, x 2 y 2 ), µ λ (y 1 (y 1 x 1 ), y 2 (y 2 x 2 ))} = min{µ λ ((x 1, x 2 ) (y 1, y 2 )), µ λ ((y 1, y 2 ) ((y 1, y 2 ) (x 1, x 2 )))} = min{µ λ (x y), µ λ (y (y x))}.

10 20 M. AKRAM AND K.H. DAR Hence µ λ is a fuzzy ideal of K K. Conversely, suppose that µ λ is a fuzzy ideal of K K. Then min{λ(e), λ(e)} = µ λ (e, e) µ λ (x, y) = min{λ(x), λ(y)} (x, y) K K. It follows that λ(x) λ(e), x K. For any x = (x 1, x 2 ), y = (y 1, y 2 ) K K, min{λ(x 1 ), λ(x 2 )} = µ λ (x 1, x 2 ) min{µ λ ((x 1, x 2 ) (y 1, y 2 )), µ λ ((y 1, y 2 ) ((y 1, y 2 ) (x 1, x 2 ))} = min{µ λ (x 1 y 1, x 2 y 2 ), µ λ (y 1 (y 1 x 1 ), y 2 (y 2 x 2 ))} = min{min{λ(x 1 y 1 ), λ(x 2 y 2 )}, min{λ(y 1 (y 1 x 1 )), λ(y 2 (y 2 x 2 ))}} = min{min{λ(x 1 y 1 ), λ(y 1 (y 1 x 1 ))}, min{λ(x 2 y 2 ), λ(y 2 (y 2 x 2 ))}}. Putting x 2 = y 2 = e gives λ(x 1 ) min{λ(x 1 y 1 ), λ(y 1 (y 1 x 1 ))}. Hence λ is a fuzzy ideal of K. References [1] M. Akram, K. H. Dar, Y. B. Jun and E. H. Roh, Fuzzy structures of K(G)-algebra, Southeast Asian Bulletin of Mathematics 31(4)(2007) [2] M. Akram and H. S. Kim, On K-algebras and BCI-algebras, International Mathematical Forum 2(9-12)(2007) [3] P. Bhattacharya and N. P. Mukherjee, Fuzzy relations and fuzzy groups, Information Sciences 36(1985) [4] K. H. Dar and M. Akram, On a K-algebra built on a group, Southeast Asian Bulletin of Mathematics 29(1)(2005) [5] K. H. Dar and M. Akram, Characterization of a K(G)-algebras by self maps, Southeast Asian Bulletin of Mathematics 28 (2004) [6] K. H. Dar and M. Akram, On K-homomorphisms of K-algebras, International Mathematical Forum 46(2007) [7] K. H. Dar and M. Akram, On subclasses of K(G)-algebras, Annals of University of Craiova, Math. Comp. Sci. Ser 33(2006) [8] Q. P. Hu and X. Li, On BCH-algebras, Math. Seminar Notes 11 (1983) [9] Y. Imai and K. Iseki, On axiom system of propositional calculi XIV, Proc., Japonica Acad 42(1966) [10] K. Iseki, An algebra related with a propositional calculus, Proc. Japan Acad 42 (1966) [11] Y. B. Jun and C. H. Park, Fuzzy ideals of K(G)-algebras, Honam Mathematical Journal 28(1)(2006) [12] J. Neggers and H. S. Kim, On B-algebras, Matematicki Vesnik 54(2002) [13] A. Rosenfeld, Fuzzy groups, J. Math. Anal. Appl. 35 (1971) [14] L. A. Zadeh, Fuzzy sets, Information and Control 8 (1965) (Muhammad Akram) Punjab University College of Information Technology, University of the Punjab, Old Campus, Lahore-54000, Pakistan address: m.akram@pucit.edu.pk (Karamat H. Dar) Govt. College University Lahore, Department of Mathematics, Katchery Road, Lahore-54000, Pakistan address: prof_khdar@yahoo.com

On Fuzzy Dot Subalgebras of d-algebras

International Mathematical Forum, 4, 2009, no. 13, 645-651 On Fuzzy Dot Subalgebras of d-algebras Kyung Ho Kim Department of Mathematics Chungju National University Chungju 380-702, Korea ghkim@cjnu.ac.kr